At the present time, recycling of minor actinides stemming from the processing of used fuels is performed via two distinct routes known under the following names:                heterogeneous recycling; and        homogeneous recycling.        
In the case of heterogeneous recycling, the minor actinides during the processing of the used fuel are separated from uranium and plutonium and are then incorporated at a high content in fuel elements comprising a non-fissile matrix distinct from the standard fuel elements of the reactor. The fuel elements comprising the minor actinides may for example consist in covering elements positioned at the periphery of the core of a reactor. This recycling route notably gives the possibility of avoiding degradation of the characteristics of the standard fuel by incorporation of minor actinides while focussing on the problems generated by these actinides on a reduced material flow.
In the case of homogeneous recycling, the minor actinides are mixed at a low content, and are distributed quasi-uniformly in the totality of the standard fuel elements of the reactor. To do this, during the processing of the used fuel, the uranium, plutonium and minor actinides are processed together in order to form oxides, which are then used in the manufacturing of said fuels.
The introduction of minor actinides in fuels intended for the reactor core is expressed by significant emission of fission gases within these fuels, and by strong alpha emission. For safety reasons, provision must therefore be made for fuels having a microstructure including a stable porosity level under irradiation, which moreover allows discharge of the fission gases and of the decay helium without any physical degradation of the fuel. The recommended porosity level for such fuels should be of the order of 14 to 16%, just as the porosity should be an open porosity.
In order to try and approach or even reach such a level, it is known how to incorporate into the fuel, significant amounts of organic blowing agents during the mixing/milling step for the aforementioned oxides. However, the durability over time of the organic blowing agents is not ensured considering the high alpha emission level generated by the presence of minor actinides. Indeed, the blowing agents presently used (such as azodicarbonamide) lose their properties very rapidly, which may generate a significant scrap rate which is difficult to manage because of the presence of minor actinides. The result of this is an impossibility of storing the mixtures intended to form the fuels and because of the degradation of the blowing agents, there is a risk of swelling of the fuel pellets before sintering, intended to enter the composition of the fuel. Consequently the result is an impossibility of obtaining fuels having controlled porosity.
Thus, considering the methods of the prior art relating to the manufacturing of fuel comprising minor actinides, the inventors set the goal of developing a method which does not have the drawbacks inherent to the use of organic blowing agents, i.e. degradation of these agents as soon as the stage for mixing precursors of the fuel and therefore impossibility of obtaining controlled porosity of the fuel.